In the field of electronic circuit packaging with the progression towards increasingly dense packages, delicate components, and increasingly finer pitch lines, the need arose to provide for reliable interconnection between a multiplicity of contact points (as for example, between circuit cards and mother boards) wherein the forces required to be exerted in order to effect such interconnections was minimized or ideally eliminated. Accordingly, connector systems were sought in the industry which avoided the destructive forces exerted by conventional systems on these delicate and dense circuit packages occurring during the act of effecting interconnections as, for example, by the insertion of a printed circuit card into a conventional edge connector.
Accordingly, from such needs arose the development of a type of connector known in the art as a zero insertion force connector. Typically, in the operation of such connectors, pins carried on a package which was desired to be interconnected to a host board, card, or the like carried a plurality of pins which were matingly received by a like pattern of holes disposed in the host receptacle. A variety of mechanical mechanisms were provided whereby once these pins were inserted into the holes, lateral forces were imparted on the pins by metallic contacts carried by the host thereby effecting the desired electrical interconnections. The holes were sized relative to the pins whereby the initial insertion force was minimal, with the primary forces necessary to effect the interconnections being side forces. The benefits of such zero insertion force connectors thus became well known whereby the risk of damage to the circuitry was certainly reduced during the interconnection operation. A representative example of such a zero insertion force connector system is described in IBM Technical Disclosure Bulletin, Vol. 17, No. 2, July 1974, pages 440-441.
Notwithstanding the development of such connector systems numerous problems still remain which were compounded by the increasingly denser modern packaging techniques. These techniques resulted in the aforementioned increasingly more delicate circuit lines and circuit packages which could not withstand the forces circuit packages were subjected to upon insertion into conventional connector systems. One problem, as is clearly evident in the hereinbefore noted connector system was the sheer mechanical complexity of these systems giving rise to reliability problems, unacceptable manufacturing costs and the like. This mechanical complexity was due in part to the need to provide for these lateral connecting forces after the initial contact between the circuit package and the host. As a result of this mechanical complexity, the density of contact points on a circuit package which might be reliably interconnected was severely restricted.
Another approach known in the art for minimizing the forces necessary to be exerted on a contact point to effect electrical interconnections employed the properties of buckling beams, the general concepts of which may be found discussed in "Engineering Mechanics of Deformation Bodies", second edition 1969, Chapter 11 by Snyder Byars. The fundamental concept was to capitalize on the property of a buckling beam that a readily constant pre-determined and controllable force was necessary to compress the buckling beam member in its longitudinal direction. Two contact points which were desired to be electrically interconnected would be urged into contact with respective ends of the beam and by further thereafter urging them towards one another, which required a relatively constant nominal force which might be pre-selected and controlled by exercising good design, the desired interconnection might be effected. This technique was employed typically, for example, in probes, used in various types of test equipment.
However several serious obstacles remained in transferring the benefits of the properties of buckling beams into the electrical connector art. First, applications of such buckling beams wherein the electrical interconnections were effected by longitudinal movement of the contact points into engagement with the buckling beam ends was typically limited to applications wherein permanent electrical interconnections were not desired but rather only ones of a temporary nature as, for example, in the case of test probes and related equipment. Although the forces required for effecting interconnections by use of the buckling beam principle were admittedly reduced from those of more conventional approaches such as those encountered in typical press fit edge connectors, means were typically not provided for maintaining these forces permanently in the context of connector systems. This is quite understandable in the application to test equipment wherein the desired interconnections are intended to be quite momentary. Furthermore, application of this technique was also typically encountered with single probes wherein again the need is for effecting only a momentary contact. Whereas it is true that for example in the connector disclosed in the aforementioned Technical Disclosure Bulletin provision is made for a plurality of such buckling beams, it is further typical that the actual mechanical interconnection to the plurality of pins was effected by means of side forces.
Furthermore, yet an additional drawback to attempted applications of buckling beams in connector systems remained. Although it is true the necessary insertion force for contact might be significantly reduced over that required by conventional systems, such force was nevertheless still required (as contrasted, for example, with the true zero insertion force connectors known in the art with their attendant mechanical complexities). With the increased density of contact points in modern electronic packaging technology, such reduced forces when multiplied by the number of necessary connections to be made still heretofore rendered the cumulative longitudinal compressional buckling forces unacceptable for the connector makeup.
For the foregoing and other reasons, an electrical connector system was long needed in the art which provided the benefits of both zero insertion force connectors as well as interconnections effected by means of buckling beams wherein the contacts might be made by contact points on the ends of circuit packages when brought into engagement with the buckling beams rather than through the conventional use of lateral forces. Such a connector system was further highly sought after which could not only provide for end point contacts, but was mechanically simply, reliable, inexpensive to manufacture, and readily adaptable to the vastly increasing contact point densities and connector requirements wherein even minute insertion forces were intolerable. These and other deficiencies of the connector systems of the prior art are overcome by the subject invention.